The present invention relates to an apparatus for rotating a cutting tool by the use of a pressurized-air. Also, the present invention relates to an apparatus for an air-driven rotating and cutting device such as drill used in medical and dental procedures and machine workings.
Japanese Patent Application JP 10-123746 (A) filed in the name of J. Morita MFG. Cooperation discloses an air-driven rotating and cutting device, or handpiece, for the medical and dental procedures and machine workings. The device employs a double-wheel rotor for effectively changing a pneumatic energy into a rotational force. The double-wheel rotor has a hub in the form of ring that is defined at an outer periphery thereof with first and second turbine wheels. The first turbine blade includes a plurality of first turbine blades each extending radially and outwardly from the center of the hub. Likewise, the second turbine wheel has a plurality of second turbine blades each extending radially and outwardly from the center of the hub.
The handpiece is formed at its head with a chamber in which an inner housing with an outer configuration in the form of cylinder and corresponding to an inner configuration of the chamber is received. In turn, the inner housing receives the rotor and a bearing mechanism for rotatably supporting the rotor. The head and the inner housing are formed with an air-supply passage for ejecting a compressed air toward the first turbine wheel of the rotor and an air-discharge passage for discharging the air from the second turbine wheel. Also, the inner housing is formed with a connecting passage for guiding the pressurized-air from the first turbine wheel to the second turbine wheel. This allows that the pressurized-air ejected from the supply passage impinges on the first turbine blades of the first turbine wheel. Then, the pressurized-air travels through the connecting passage to the second turbine wheel where it also impinges on the second turbine blades and then discharged through the discharge passage to the atmosphere.
As described above, the handpiece with the double-wheel rotor allows the energy of the pressurized-air to be used most effectively at the two turbine wheels. This results in that the drill can be rotated in a high speed with an elevated torque feature than the conventional handpiece with a single-step rotor.
In this handpiece with double-wheel rotor the cylindrical part of the inner housing has a plurality of slots formed in its certain peripheral area for defining the connecting passages of the inner housing. Also, the slots are closed at outer openings thereof by a closure in the form of ring that surrounds the inner housing. Disadvantageously, the arrangement needs the additional closure or ring. In addition, in order to secure the ring to the cylindrical housing, screw threads should be machined in the opposing outer and inner surfaces of the cylindrical housing and the ring, respectively. Besides, a possible gap between the cylindrical housing and the ring results in a leakage of the pressurized-air, deteriorating the effective use of the energy derived from the pressurized-air and then the stability in the rotational number and the torque of the rotor.
Indeed, the handpiece results in the higher torque even at the high rotational number. This means that the double-wheel rotor is the most effective device for the dental handpiece that is required to rotate the cutting tool at about 300,000 to 500,000 rpm. On the other hand, another requirement has been existed to slightly decrease the rotational number while maintaining the high torque.
For example, for the dental handpiece, a slight decrease of the rotational number will result in various advantages. For example, heat generated at the cutting of the tooth is decreased, which is effective for cushioning a toothache possibly caused by the heat and also avoiding pulpitis possibly caused by the heat increase of the pulp. Also, noises generated at the cutting are decreased and the noises with higher frequencies are also reduced. In particular, the noises generated by the rotations of the rotor and cutting tool at the procedure, in particular noises with high frequency, may provide the patient with a fear against the procedure. Further, the high speed rotation, for example, at about 300,000 to 500,000 rpm, may damage the elongated dental cutting tool even by a slight increase of the load at the cutting of the tooth. On the contrary, a possibility of the damage will be reduced considerably even by a slight decrease of the rotational number, for example, 10,000 to 50,000 rpm. Furthermore, a slight decrease of the rotational number of the cutting tool, for example, from about 300,000-500,000 rpm by about 10,000-50,000 rpm, results in a considerable extension of a durability of a bearing mechanism, in particular ball bearing, of the dental cutting tool.
In addition, in the above-described double-wheel rotor the first and second turbine wheels are positioned along the central axis of the rotor, which results in the enlargement in size of the head of the handpiece in that direction. However, the size of the head in that direction is restricted in the handpieces for children and aged persons. This requires another technique to be developed to realize the high speed and high torque handpiece with small head incorporated with the double-wheel rotor.
Besides, in the handpiece with double-wheel rotor the passage for the supply of air to the rotor is defined by a plurality of parts. This requires a variety of parts to be prepared and then assembled together in the manufacturing of the handpiece. This also causes small gaps between the neighboring parts, which result in a leakage of the pressurized-air and also a deterioration of effectiveness in the energy change of the pressurized-air into the rotation of the rotor.
Accordingly, an air-driven rotating and cutting device comprises a rotor having a rotational axis and detachably holding a cutting tool in the rotational axis. The rotor is formed with first and second turbine wheels. The first and second turbine wheels are formed with first and second blades, respectively. Also, each of the first blades defines a first channel with adjacent first blade therebetween and each of the second blades defines a second channel with adjacent second blade therebetween. The device further includes a housing for receiving the rotor for rotation about the rotational axis. The housing has channels for fluidly connecting the first and second channels, so that an air is guided from the first channels through the connecting channels to the second channels as the rotor rotates. Further, each of the connecting channels is defined by an opening opened toward a direction parallel to the rotational axis and a surface portion formed by extending the opening to a direction along the rotational axis.
With the arrangement, the connecting channels are formed or machined only from the direction parallel to the rotational direction without tilting or changing working direction, causing the head with the connecting channels to be manufactured without any difficulty and thereby inexpensively. The conventional housing has slots extending between the inner and outer surfaces, which decreases the strength of the housing as well as the durability thereof. Contrary to this, according to the present invention, since the housing is free from such slots, it has a greater strength than the conventional one. Also, the connecting channel in the conventional device is formed by two separate members (i.e., inner housing and the ring) which should be assembled together. However, the connecting channels in the device of the present invention are formed in the single member. This causes the device to be manufactured more easily and prevents the pressurized air from leaking, which stabilizes the rotational number and the torque of the rotor.